1. Field of the Invention
The invention relates to methods used to assess and report structural health and, more particularly, to methods used to automatically assess and report structural health.
2. Description of the Related Art
As a structure (e.g., an aircraft, building, truck, etc.) ages or as repairs to the structure age, non-destructive evaluation may be performed to verify the health of the structure and to confirm that the structure has sufficient remaining strength for continued operations. Structural damage data (e.g., data from non-destructive evaluation) must be interpreted in order to assess the health of a structure. Present technology requires that an operator (a person) interpret this data. Errors can arise due to manual collection and interpretation of the data, leading to errors in assessment of the health of a structure.
Variability exists when data from non-destructive inspection of structural components is interpreted manually. For any given structural inspection task, the probability of detection (PoD) is affected by several factors. These factors include: 1) the skill and experience of the inspector, 2) accessibility to the structure, 3) exposure of the inspection surface, and 4) confounding attributes such as underlying structure or the presence of rivets. This variation can cause missed flaws (false negatives) and over-reported flaw sizes (false positives). One source of the variation is the manual interpretation of inspection data.
Costs associated with false negatives and false positives have the potential to be high. At present, very conservative structural design is one way of managing the uncertainty surrounding inspection data. When these concepts are applied to bonded structural repairs, allowable damage limits (flaw sizes) for bonded repairs can be tied to inspection system capabilities and made to be so conservative that the benefit of the repair is not realized.
Consequently, present structural inspections require a combination of sophisticated equipment and operator experience and knowledge to obtain an assessment of structural health. Errors in the assessment of structural health may have undesirable economic consequences.
Due in part to these consequences the “Ramp Damage Checker” (disclosed in US 2005/0279171) was developed for the airline industry. This device determines if the structure has hidden damage. However, the impact of the detected damage on the structural strength is not determined.
Other attempts at combining non-destructive inspection (NDI) data and analysis have been made. The Structural Repair of Aging Aircraft (SRAA) program provides an example of this concept (Contract awarded to Boeing by the Air Force Research Laboratory, contract no. F33615-98-2-5113). The method used by the SRAA program was to modify a structural model based on NDI data. The model modifications were performed manually by the operator aligning the NDI data with the existing structural model.
Accordingly, there is a need for a method to automatically assess and report structural health.